js 识别ios和Android

var u = navigator.userAgent, app = navigator.appVersion;
        var isAndroid = u.indexOf('Android') > -1 || u.indexOf('Linux') > -1; //g
        var isIOS = !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/); //ios终端
        if (isIOS) {
            alert("ios");
        }
        if (isAndroid) {
            alert("Android");
        }